ABSTRACTIn the field of investigating fracture mechanisms, an intensive co-operation between earth seismologists and civil engineers has been existing for more than ten years. Numerous procedures of earthquake analysis and other seismological phenomena were transferred to material sciences, since the parallels to acoustic emission analysis are evident. Besides an accurate localization of fracturing an inversion on the moment tensor is performed. The moment tensor contains all information about the stress release during a rupture process, like the total energy and the orientation of rupture planes. Several methods for an inversion on this tensor are in use by seismologists today. After a suitable decomposition of the moment tensor, the type of the rupture process can be quantified and visualized using ostensive crack models, like those for shear and explosion. However, common methods of moment tensor inversion from acoustic emission data face various limitations, though relative methods were successfully applied before. In this article some theoretical principles on the decomposition of the moment tensor are reviewed. An adaptation of the physical theory to common crack models in material sciences, is discussed. Furthermore, a major influence of size effects caused by the dimensions of the specimen, the relative distance between source and receiver, or the size of the crack

AbstractAcoustic emission data contains a lot of information about the fracture process it was emitted from. A quantitative acoustic emission analysis permits detailed investigations on the fracture mechanics and the failure process. But often there are several thousand events from one fracture area. Doing the data analysis by hand is a very time consuming process and therefore often only a rudimentary analysis is performed. Furthermore, the data's signal to noise ratio is often very low. Therefore, the development of an automatic analysis method containing data conversion, de-noising, localization, moment tensor inversion and other features from the field of statistical mathematics is indispensable. The general analysis concept is based on the model-view-controller (mvc) paradigm which is realized by using different development environments. Therefore, the software development packages MATLAB and LabVIEW were used. The connection of these two programmes via so called 'Formula Nodes' makes a fast development possible because the advantages of both packages can be used. Furthermore, external code (source code or dynamic link library) can be linked to the analysis environment. A good balance between transparency and automation of the processing steps themselves and the entire acoustic emission analysis should be reached.Key words:acoustic

ABSTRACTIn the field of investigating fracture mechanisms, an intensive co-operation between earth seismologists and civil engineers has been existing for more than ten years. Numerous procedures of earthquake analysis and other seismological phenomena were transferred to material sciences, since the parallels to acoustic emission analysis are evident. Besides an accurate localization of fracturing an inversion on the moment tensor is performed. The moment tensor contains all information about the stress release during a rupture process, like the total energy and the orientation of rupture planes. Several methods for an inversion on this tensor are in use by seismologists today. After a suitable decomposition of the moment tensor, the type of the rupture process can be quantified and visualized using ostensive crack models, like those for shear and explosion. However, common methods of moment tensor inversion from acoustic emission data face various limitations, though relative methods were successfully applied before. In this article some theoretical principles on the decomposition of the moment tensor are reviewed. An adaptation of the physical theory to common crack models in material sciences, is discussed. Furthermore, a major influence of size effects caused by the dimensions of the specimen, the relative distance between source and receiver, or the size of the crack

AbstractExisting instruments designed for measurements involving the Impact-Echo technique are usually of limited use in field tests when investigating large concrete structures like buildings or tunnels. In 2001 demand for such instruments increased dramatically particularly in Germany, as German authorities made quality control tests of state road tunnel constructions mandatory. For this task, it is essential that the equipment used for Impact-Echo measurements along profiles uses the scanning technique and is easy to work with.Together with the Institute of Construction Materials of the University of Stuttgart, develogic GmbH has developed a new concept for Impact-Echo testing systems. On the hardware side, an impactor generates very short transient waves. Single manual "shots" can be generated as well as repetitive impacts. A handheld (one hand control) and a stand-alone version are available. There is an external computer control via TTL (Transistor-Transistor-Logic). The device is small and easy to handle, robust and mobile. It is designed for rough environments - a water-proof version for underwater testing is also available on request. A TTL output triggers at the exact moment of impact onto the structure to be tested. Apart from the basic version of the impactor, an electronic version utilizing programmable impact intervals

AbstractThe application of wavelets on time series in a general sense is more than 15 years old. Applications that are making use of wavelets include signal and image processing, optics, fractals, seismology and acoustics. Wavelets are mathematical functions that cut up data into different frequency components, and then study each component with a resolution matched to its scale. Wavelet analysis is capable of revealing aspects of data that other signal analysis techniques miss. This makes wavelets interesting and useful for acoustic emission analysis. The acoustic emission signal caused by microscopic movements contains a lot of information about the fracture process but also usually a significant amount of noise. The wavelet shrinkage and thresholding methods allow recovering the signal from noisy data. De-noising is possibly the most popular practice of wavelets on data because after decomposing the signal the further process is rather intuitive. The basic methods used for signal decomposition are the discrete and the continuous analysis. The use of discrete or continuous decomposition techniques depends on the complexity of the signal. In fact, de-noising is a powerful but not the only application of wavelets on time series. They can be used for statistical methods like density estimation and detection of self-similar behavior in time series. Wavelets show an

Improvement and Application of NDT Methods in Civil Engineering in the Frame of a Collaborative Research Project funded by the German Research SocietyC. Grosse108, H. Reinhardt31aInstitute of Construction Materials bInstitut für Werkstoffe im Bauwesen; University of Stuttgart271, Stuttgart , GermanyNDT-wide, civil engineering

AbstractA collaborative research project (FOR 384) has been founded in Germany. The aim of the FOR 384 is the methods for investigating concrete structures to improve in such a way that the systematic application of NDT diagnosis is possible and the validation for many tasks is achievable. The isolated developments so far should be innovated thus that a cooperative long-lasting cooperation in working groups is possible. Acoustic and electro magnetic methods for the investigation of structures made of concrete will be checked. The members of the FOR 384 and their supporters from practical engineering and the industry try to understand the processes and mutual interdependencies in order to put the methodology of such investigations on a objective scientific basis.Keywords:Research cooperation, NDT on severe structures, modern NDT methodsOrganisation and members of the research group FOR 384The German Research Society (DFG) has introduced net-based collaborations in the year 2000. Such a cooperation can consist of researchers of all parts in Germany. Table 1 shows the composition of the group and the members of the so-called supporting groups from the industry.<

AbstractA testing device based on ultrasonic techniques was developed to analyze the setting and hardening of cement-based materials. This method is able to document and analyze the setting and hardening process continuously in a way that could not be achieved by conventional techniques such as the vicat-needle test, the penetrometer test, the slump test, or rheologic testing methods.In this paper experiments with several newly developed or modified testing devices are presented. The focus of this development was set to the elimination of some disadvantages of typical other concrete ultrasound devices as well as an improvement of the handling and cost efficiency. A progress was made regarding the ultrasound emitter, where two different concepts were tested: one is basing on an impact producing short transient ultrasound pulses of broad frequency content. The second approach uses broadband ultrasound transducers as an emitter applied in combination with power-amplifiers.The second part of this paper addresses tests performed during round robin tests. This is in the frame of the RILEM (Réunion Internationale des Laboratoires d'Essais et de Recherches sur les Matériaux et les Constructions) Technical committee 185-ATC, working in the field of advanced testing of cement-based materials

ABSTRACTAt a New Zealand wastewater treatment plant there are several large wastewater settlement tanks that are crucial to the operation of the plant. These concrete tanks are 50 metres in diameter and 8 metres deep with the base of each tank approximately seven metres below ground level.It was discovered that the base of one of the tanks had become distorted, with the result that it could no longer carry out its function. This was a major problem for two reasons:1. The tank was important for maintaining sufficient throughput for the overall operation. 2. There was a danger of contamination of the subsurface aquifers, which are the main potable water supply for the area, should a tank base failure occur.In addition to the problems outlined above, due to the type of construction of these tanks, the floor could not be cut into or disturbed to any significant extent without risking catastrophic failure.Ground penetrating radar (GPR) was used to accurately pinpoint those areas below the base of the tank where voids had formed; the subsurface voids were the root cause of the tank floor distortion. The information that was provided using ground penetrating radar enabled grouting